It is known that a perpendicular magnetic recording system is theoretically possible to record a higher density than a longitudinal magnetic recording system. The perpendicular magnetic recording system has been researched for many years. It was confirmed that the perpendicular magnetic recording system could record 600 kFCI (Flux Change per Inch) or more.
The perpendicular magnetic recording system has a problem on reproduction. A magnetic leakage flux output from a magnetic recording medium is not enough to reproduce. The problem is bigger in a hard disk apparatus which a flying magnetic head is utilized as a magnetic reproducing head, because the magnetic head reproduces a magnetic signal while not contacting a magnetic recording medium. A high reproducing sensitivity is necessary to put the perpendicular magnetic recording system to practical use.
For this purpose, the following perpendicular magnetic recording system is researched. In this system, the magnetic recording medium is utilized, which has a high permeability layer between a magnetic recording layer and a substrate. A single pole piece magnetic head is also utilized, which an auxiliary magnetic pole piece is provided in parallel with a main magnetic pole piece. The high permeability layer of the recording medium and the auxiliary magnetic pole piece of the single pole piece magnetic head form a closed magnetic circuit. For example, a paper such as "Journal of the Magnetic Society of Japan Vol. 15 Supplement, No. S2(1991), pp875-880" was published. A sufficient reproduction level is not obtained even in this paper.
The enlarged sectional view of this magnetic head is FIG. 6. A main magnetic pole piece 5 is disposed through an underlayer 2 such as Al.sub.2 O.sub.3 on a non-magnetic substrate 1. Part of the main magnetic pole piece 5 is thick to increase a magnetic permeance (6). A coil conductor 8 is formed in a certain pattern through an insulating layer 7 on the main magnetic pole piece 5. An auxiliary magnetic pole piece 9 is disposed through the insulating layer 7 above the main magnetic pole piece 5. Part of the auxiliary magnetic pole piece 9 is connected to the main magnetic pole piece 5 to construct the closed magnetic circuit. A head surface 10 opposite to a magnetic recording medium is polished so as to expose the main magnetic pole piece to the head surface 10.
A magnetoresistance effect element (MR element) may be utilized to increase a reproduction sensitivity in a reproducing head. There are two types of magnetoresistance effect heads, a shield type head and a yoke type head. They are known in a longitudinal magnetic recording system. "IEEE TRANSACTIONS ON MAGNETICS, vol.24, No.6, Nov.(1988), pp2612-2614" discloses the shield type head. "OYOJIKIGAKKAI JIKIKIROKUKENKYUKAI SHIRYOU MR84-44, pp19-24" discloses the yoke type head. Japanese Laid Open Patent HEI 2-128312 and Japanese Laid Open Patent HEI 3-171410 disclose examples applying these heads to the perpendicular magnetic recording system.
These examples may be difficult to obtain enough magnetoresistance sensitivity because of the disposition of the MR element. They may also lose a recording efficiency. Further, these examples are not able to obtain the peculiar effect to the perpendicular magnetic recording which increases the recording efficiency by a closed magnetic circuit constructed between a high permeability layer of a magnetic recording medium and a magnetic head.
The example disposing the MR element in the shield type head is shown in FIG. 7. A pair of shields being magnetic layers are disposed through an underlayer 2 such as Al.sub.2 O.sub.3 on a substrate 1. A MR element 3 and a bias layer 4 being a conductive layer are disposed through an insulating layer between the shields 11. A main magnetic pole piece 5, a thick part of the main magnetic pole piece 6, a coil conductor 8, an auxiliary magnetic pole piece 9 for a recording head are disposed through the insulating layer as shown in FIG. 7. The MR element 3 and the main magnetic pole piece 5 of the recording head is exposed to the head surface 10 opposite to a magnetic recording medium.
In this example, because the MR element 3 is provided near the head surface 10, the high sensitivity is obtained. But because the MR element 3 is exposed to the head surface 10, the characteristics may be changed because of a contamination. It makes the reliability decline.
Further, this shield type head has the following problem. Because there is no auxiliary magnetic pole piece for the reproducing head, the closed magnetic circuit is not formed between the high permeability layer of the magnetic recording medium and the reproducing head. Because it is necessary to laminate the recording head and the reproducing head respectively, the construction becomes complicated. It is also a problem that the starting point of reproducing on the reproducing head is different from the starting point of recording on the recording head. When the head is moved by a rotation arm, the position reproduced by the reproducing head slips off the position recorded by the recording head in the direction of the track width.
The enlarged sectional view which a MR element is provided in the yoke type head is shown in FIG. 8. Part of the main magnetic pole piece 5 and the thick portion 6 of the main magnetic pole piece are cut off and a MR gap is formed at the cut off portion. The MR element 3 and the bias layer 4 are provided at the MR gap. This example has the following advantage and problems. Because the MR element is provided not to be exposed to the head surface, the reliability becomes high. But the sensitivity becomes low. The MR gap 12 is formed in the closed magnetic circuit. The MR element 3 having a high reluctance is provided in series with the closed magnetic circuit. So the closed magnetic circuit does not work enough and the signal magnetic flux is not led to the main magnetic pole piece efficiently.